This invention relates to a process for the breeding of aquatic animals in a controlled environment wherein the aquatic animals are maintained in water reservoirs which are open only to the atmosphere and which have water flowing therethrough constantly or intermittently, and wherein the oxygen content of the water present in the water reservoirs is kept at a value corresponding to the optimum rearing conditions for the aquatic animals by the introduction of a gas consisting essentially of oxygen or oxygen-enriched air.
A process for fish farming has been known from DOS [German Unexamined Laid-Open Application] No. 2,110,091 wherein oxygen-enriched water, pumped preferably from a spring or from a well, is conducted continuously from the bottom toward the top through a vertically disposed container constituting the living space for the fish and, in order to attain optimum rearing conditions, oxygen or an oxygen-containing gas is fed into the container from the bottom.
The water current, oriented from the bottom toward the top in the container serves, in this system, for discharging the metabolic wastes produced by the fish, or other waste matter, with the overflow water discharged at the top edge of the container. To be able to maintain this flow direction of the water at all times, it is consequently necessary to introduce also the gas to be fed for the oxygen enrichment of the water always in the same flow direction as the water into the container.
However, as a consequence thereof, this process operates uneconomically with respect to the utilization of the thus-introduced oxygen. This is so, because due to the same flow direction of water and gas, the residence time of the thus-fed oxygen bubbles within the water, which residence time is additionally dependent on the flow velocity of the water and of the gas required to discharge the metabolic wastes, is too short along the dissolution distance predetermined by the height of the container to permit the complete dissolution of such bubbles. Accordingly, undissolved oxygen escapes into the atmosphere at the top edge of the container. Furthermore, it is impossible to provide a higher oxygen content in the water, which becomes necessary with the increasing growth of the fish, by the introduction of an arbitrarily larger oxygen stream. Apart from the fact that the oxygen utilization in such a case is even less than before, an increased oxygen stream leads to turbulent water currents within the container, resulting in a dropping of the fecal waste to the bottom of the container in opposition to the water current. As a consequence, the oxygen feed means are clogged up, on the one hand, and poisoning phenomena occur in the fish and the flavor of the fish is impaired, on the other hand.